This specification claims priority to German Patent Application No. 199 16 267.0, filed on Apr. 12, 1999 and PCT/EP00/03007, filed on Apr. 5, 2000.
The present invention relates to a method and a device for monitoring or for influencing the movement of a vehicle on a path.
The driver controls the movement of a vehicle according to a path to be followed. This is mainly done by way of the steering system of the vehicle. If the driver is inattentive, the vehicle can escape from the path. Different, so-called xe2x80x98lane-keeping systemsxe2x80x99 which intervene directly into the steering of a vehicle to counteract this tendency are known in the art. In these systems, e.g. the housing of the steering gear is displaced, or an additional steering torque is applied to the steering system by way of an electric motor. It is, however, disadvantageous in these systems that the steering system no longer reacts as the driver is used to or desires. The result is that the driver can no longer govern the vehicle completely.
In view of the above, an object of the present invention is to disclose a method and a device for monitoring or influencing the movement of a vehicle on a path which does not intervene into the steering system of the vehicle, with the driver maintaining full control over the vehicle.
The method for monitoring or influencing the movement of a vehicle on a path first of all includes determining a desired path to be followed by the vehicle. This determination may be effected by way of appropriate optical sensors, such as infrared sensors or a video camera which, for example, detect the roadway tracks or a vehicle driving in front, and forward corresponding signals, for example, to an image processing system determining therefrom the desired path, such as the space coordinates with respect to the vehicle coordinates. The desired path can be a local position, a sequence of dots, a vector, or a trajectory.
Further, the actual movement of the vehicle is determined. This may refer to the steering angle, the yaw velocity, or the transverse acceleration, that means, the respective components about the vertical axis of the vehicle, or also corresponding components in the longitudinal vehicle direction. Thus, the actual movement can depend on a number of parameters or may have several components. The sensor means required to determine the actual movement can be provided by a known ESP sensor system (Electronic Stability Program).
Thereafter follows a comparative analysis of the desired path and the actual movement which may preferably be performed in two ways: on the one hand, a desired movement can be determined from the desired path which the vehicle is to perform for maintaining the desired path. Subsequently, a comparison can be made between the desired movement and the actual movement which furnishes a difference in movement as a result. Another possibility involves extrapolating from the actual movement an xe2x80x98actual pathxe2x80x99 which the vehicle would follow due to the actual movement. Subsequently, a comparison can be made between the desired path and this actual path which furnishes a difference in path as a result.
The present invention offers two possibilities of utilizing the result of the comparative analysis.
During monitoring the movement of a vehicle an information variable is determined on the basis of the difference (result) and forwarded to the driver of the vehicle by haptic means, meaning through physical including tactile means. This is preferably done by way of the steering wheel of the vehicle, thereby communicating in a tactile manner through the hands of a driver which are generally very sensitive. The information variable can provide a proposal of direction for steering of the vehicle so that the driver receives a hint as to steering the vehicle towards the desired path. Besides, the information variable can furnish a proposal for the intensity, i.e., the speed of steering. Thus, the driver is e.g. required to countersteer the more (the faster) the vehicle deviates from the desired path. Also, it must be taken into account that the desired path determined not always is the ideal path or the path the driver wishes to follow. Therefore, it is up to the driver to utilize the information transmitted to him/her in order to guide the vehicle to the desired path or to steer the vehicle to any other path desired.
At least one wheel brake is actuated according to the difference when influencing the movement of a vehicle is intended. The said wheel brake is preferably a wheel brake on the front axle of the vehicle because there the portion of the entire braking effort of the vehicle roughly amounts to 70 to 80%. Preferably, the brake pressure on the wheel brake is increased to steer the vehicle into a different direction, for example, towards the desired path. When the vehicle has already slowed down, it is also possible to raise, the brake pressure on one wheel brake and to decrease the brake pressure on the other wheel brake of the same axle. Preferably, the decrease and the simultaneous increase of the brake pressure takes place so that the vehicle is not braked less than before.
Brake pressure increase can amount to less than 30 bar, and the speed of the brake pressure increase (brake pressure gradient) can range from 10 to 20 bar/s. The effect is that the driver senses only a slight steering deviation of the vehicle, yet the vehicle does not deviate substantially from its current path. The driver is thereby only informed that he/she is leaving the desired path determined. However, the driver is now as before able to fully control the vehicle and continue steering the vehicle as he/she desires.
When the driver is diverted and therefore leaves the desired path, it can be expedient to alarm him/her. This can be done by abrupt braking which can be achieved by a brake pressure gradient that exceeds 100 bar/s. This causes the vehicle to be braked to a stronger extent for a brief interval which is unpleasant to the driver so that upon receiving this tactile input, he/she xe2x80x98wakes upxe2x80x99 and pays attention to the driving operation again.